# Last edited on 2010-06-27 12:50:56 by stolfi

GOAL

  Investigate the non-uniformities of the imaging response of the AVT
  Pike F-100 camera made available to Rafael Saracchini at MVL-UWE in
  may-jun 2010.
  
  The main sources of non-uniformity seem to be:
    
    (1) Vignetting by the lens. Should have radial symmetry.
  
    (2) Variation in pixel gains. There seem to be both high- and
    low-frequency variations.
    
    (3) Gain difference between the two sensor output amplifiers used
    for left and right halves of the image.

  Item (3) the difference in brightness between the two halves of the
  sensor was corrected by setting the gains of the two output
  amplifiers to the same value (the default was wrong).
  
  Now we will try to extract a white mask to compensate for (1) and (2).

PROCEDURE

  Rafael at UWE took some images of a paper sheet with unfocused lens
  and LED-1 lamp, with light source at various azimuths and with
  various shutter times.
  
  The Pike F-100 RAW16 images have been fecthed and renamed (see
  "data/wget-images.sh").  The names are "data/t-${light}-${shutter}.raw"
  where ${light} is
  
    "a000d0" azimuth   0 inclination 25 degrees
    "a090d0" azimuth  90 inclination 25 degrees
    "a180d0" azimuth 180 inclination 25 degrees
    "a180d2" azimuth 180 inclination 25 degrees with paper displaced 2cm
    
    lights=( "a000d0" "a090d0" "a180d0" "a180d2" )
    
    
  The first three sets were obtained with the paper sheet and camera
  at exactly the same position.  The ${shutter} parameter is 
  
    shutters=( "s4095" "s3072" "s2048" "s1024" )
    
  Extracting the Bayer channels split into two halves:
  
    for light in ${lights[@]} ; do
      for shutter in ${shutters[@]} ; do 
        for chn in G0 G1 R0 B0 ; do 
          piketopnm -crop 0 0 502 1000 -extract ${chn} \
            < data/t-${light}-${shutter}.raw \
            > out/t-${light}-${chn}-h0-${shutter}.pgm 
          piketopnm -crop 502 0 498 1000 -extract ${chn} \
            < data/t-${light}-${shutter}.raw \
            > out/t-${light}-${chn}-h1-${shutter}.pgm 
        done
      done
    done
  
  Fitting a linear model to the images as a function of shutter value:
  
    for light in ${lights[@]} ; do
      for chn in G0 G1 R0 B0 ; do 
        for half in h0 h1 ; do 
          pname="out/t-${light}-${chn}-${half}"
          tmp="/tmp/$$"
          echo "pname = '${pname}'  tmp = '${tmp}'"
          pargs=()
          tfiles=()
          for shutter in ${shutters[@]} ; do 
            iname="out/t-${light}-${chn}-${half}-${shutter}"
            tname="${tmp}-${light}-${chn}-${half}-${shutter}"
            pnm_to_fni -min 0 -max 1 < ${iname}.pgm > ${tname}.fni
            shval=`echo "${shutter}" | tr -d 's'`
            pargs=( "${pargs[@]}" -image ${shval} / 4095 "${tname}.fni" )
            tfiles=( "${tfiles[@]}" "${tname}.fni" )
          done
          echo "pargs = '${pargs[@]}'"
          # Fit linear model:
          fni_lin_fit \
            "${pargs[@]}" \
            -scale 65535 \
            -gain   ${pname}-g.fni \
            -offset ${pname}-o.fni \
            -origin ${pname}-s.fni \
            -verbose
          rm -f ${tmp}-*.fni
        done
      done
    done
    
  Ploting histograms: 
    
    for light in ${lights[@]} ; do
      for chn in G0 G1 R0 B0 ; do 
        for half in h0 h1 ; do 
          cname="out/t-${light}-${chn}-${half}"
          for ps in g.256 o.16 s.16 ; do 
            param="${ps%.*}"
            step="${ps#*.}"
            pname="${cname}-${param}"
            fni_hist -range -100000 100000 -step ${step} \
              <  ${pname}.fni \
              > ${pname}-hist.eps && \
              gv ${pname}-hist.eps
          done
        done
      done
    done
    
  Displaying the parameters: 
    
    for light in ${lights[@]} ; do
      for chn in G0 G1 R0 B0 ; do  
        for half in h0 h1 ; do 
          cname="out/t-${light}-${chn}-${half}"
          fni_to_pnm -min 0 < ${cname}-g.fni | convert PPM:- ${cname}-g.png 
          fni_to_pnm -center 0 < ${cname}-o.fni | convert PPM:- ${cname}-o.png 
          fni_to_pnm -center 0 < ${cname}-s.fni | convert PPM:- ${cname}-s.png 
          display -title '%f' ${cname}-{o,g,s}.png
        done
      done
    done
    
  Comparing the gains with different lightings:
  
    fni_to_pnm -min 0 -max 65535 < out/t-a000d0-G0-h0-g.fni > out/t-a000d0-G0-h0-g.pgm
    fni_to_pnm -min 0 -max 65535 < out/t-a180d0-G0-h0-g.fni > out/t-a180d0-G0-h0-g.pgm
    pnmxarith -scale 0.5 -divide out/t-a000d0-G0-h0-g.pgm out/t-a180d0-G0-h0-g.pgm > out/t-a000d0-over-a180d0-G0-h0-g.pgm
    display -title '%f' out/t-a000d0-G0-h0-g.pgm  out/t-a180d0-G0-h0-g.pgm out/t-a000d0-over-a180d0-G0-h0-g.pgm
    pnm_to_fni -min 0 -max 65535 < out/t-a000d0-over-a180d0-G0-h0-g.pgm > out/t-a000d0-over-a180d0-G0-h0-g.fni
    fni_hist -range -10000 100000 -step 16 < out/t-a000d0-over-a180d0-G0-h0-g.fni > out/t-a000d0-over-a180d0-G0-h0-g-hist.eps
    gv out/t-a000d0-over-a180d0-G0-h0-g-hist.eps
  

JUNK

  Attempt to analyze the gain discontinuity at column 500
  (actually 502)

  We extract columns 499 and 500 as a single ASCII PPM file
  with one pixel per row and a blank line after each scanline.
  More precisely we take columns 249 and 250 from Bayer channels
  G0 and G1:
  
    for exp in 0 1 2 3 4 ; do 
      for chn in G0 R0 B0 G1 ; do 
        iname="data/t_00${exp}"
        oname="out/t_00${exp}-${chn}-249-250"
        piketopnm -extract ${chn} < ${iname}.raw \
          | pnmnoraw \
          | pnmcut 0 251 500 2 \
          > ${oname}.pgm
        display ${oname}.pgm
        plot-two-col-pgm.sh ${oname}.pgm
        display ${oname}-plot.png
      done
    done
  
  Comparing the gains of two images taken under identical conditions
  of lighting (only with paper shift):
  
    for disp in d0 d2 ; do
      convert out/t-a180${disp}-G0-h0-g.png -crop '64x64+80+120' out/t-a180${disp}-G0-h0-g.pgm
    done
    plot-compare-pgms.sh out/t-a180d0-G0-h0-g.pgm out/t-a180d2-G0-h0-g.pgm > out/t-a180d0-a180d2-G0-h0-g.png
    display out/t-a180d0-a180d2-G0-h0-g.png